The present invention relates to an automated blood pressure measuring apparatus and method. More specifically, the present invention relates to an automated, non-invasive blood pressure (NIBP) monitor that includes optimized operation for use with pregnant patients, particularly those that are diagnosed as pre-eclamptic, to provide more accurate measurements of the patient's blood pressure.
Automated blood pressure monitoring has rapidly become an accepted and, in many cases, essential aspect of patient care. Such automated monitors are now a conventional part of the patient environment in emergency rooms, intensive and critical care units, and in fetal monitoring systems.
The oscillometric method of measuring blood pressure involves applying an inflatable cuff around an extremity of the patient's body, such as the patient's upper arm. The cuff is inflated to a pressure above the patient's systolic pressure and the cuff pressure is then reduced either continuously or incrementally in a series of small steps. A pressure transducer in communication with the blood pressure cuff measures the cuff pressure, including pressure fluctuations resulting from the beat-to-beat pressure change in the artery under the blood pressure cuff. The data obtained from the pressure transducer is used by a processor within the NIBP monitor to compute the patient's systolic pressure, mean arterial pressure (MAP) and the diastolic pressure.
An example of the oscillometric method of measuring blood pressure is shown and described in U.S. Pat. Nos. 4,360,029; 4,394,034; and 4,638,810, which are commonly assigned with the present invention.
Although NIBP monitors and methods, such as the oscillometric method described above, are effective in determining the blood pressure of a patient, the algorithms used within the processor of the NIBP monitor often provide marginally lower measurements for the blood pressure within high-risk obstetric patients, such as those suffering from pregnancy-induced hypertension and pre-eclampsia. Pregnancy-induced hypertension is hypertension that develops as a consequence of pregnancy and regresses after delivery. Pre-eclampsia is a type of pregnancy-induced hypertension characterized by progressive hypertension and pathological edema.
During pre-eclampsia, the physical characteristics of a patient's vascular system change, which can affect the accuracy of an NIBP monitoring algorithm that was tested in normotensive pregnant patients. As an example, the normal algorithm used to estimate both the systolic and diastolic blood pressure in a patient being monitored by an NIBP system calculates the systolic and diastolic pressures based upon a ratio from the determined mean arterial pressure (MAP). In an obstetric patient suffering from pre-eclampsia, these ratios used to estimate the systolic and diastolic blood pressure in an NIBP monitor tend to result in blood pressure measurements that are slightly lower than the manual blood pressure measurements taken by a physician utilizing a blood pressure cuff and a stethoscope. Since physicians are accustomed to treating patients based upon the manual blood pressure measurements taken using a blood pressure cuff and stethoscope, the underestimation of both the systolic and diastolic pressure when utilizing an automated NIBP monitoring system may not indicate the onset of pre-eclampsia at the same stage as would have been determined utilizing the manual blood pressure cuff and stethoscope determination technique.
Recently, studies have determined that the end tidal carbon monoxide (etCO) levels in pregnant women are lower when the women have gestational hypertension and/or pre-eclampsia as compared to a normotensive pregnant patient. Kreiser, D et al End tidal carbon monoxide levels are lower in women with gestational hypertension and pre-eclampsia. J Perinatol, Apr. 1, 2004; 24(4): 213-7. As an example, the etCO values in women suffering from pre-eclampsia were less than or equal 1.6 ppm in 89% of the patients suffering from pre-eclampsia as compared with only 45%, 54% and 46% of non-pregnant, first and third trimester normotensive pregnant women. Thus, the results of the study indicate that the etCO levels in women with gestational hypertension or pre-eclampsia were significantly lower than normotensive pregnant women. Thus, the low levels of carbon monoxide in pregnant women is believed to be an indication of pregnancy-induced hypertension and pre-eclampsia, which can be utilized in addition to a typical blood pressure measurement for a clinician in diagnosing the disorder.